Compressed fiber absorption device and method of making



July 29, 1958 A. vii. LEWING COMPRESSED FIBER ABSORPTION DEVICE AND METHOD OF MAKING Filed June a, 1953 ATTORNEYS United States Patent Q.

Albert W. Lewing, Manson, Mass,

Incorporated, Palmer, Mass., ware Application June 8, 1953,-Serial No. 360,072 12 Claims. (Cl. 128- 285) assignor to Tampax, a corporation of Delta- This invention relates to devices adapted for fluid absorption and retention, and more particularly to such devices including a compressed mass of unspun cotton and like absorbent fibers such as surgical pads, dental rolls, catamenial pads, gun wadding, nasal and vaginal tampons, and the like (all of which will be referred to generally as absorbent pads) in which the fluid absorbing medium comprises a shaped mass of absorbent cotton or like absorbent fibers. This application is a continuationin part of applications Serial Nos. 188,921 and 188,935, both filed October 7, 1950, and now abandoned.

With such absorbent pads, and especially with tampons, it is usually desirable that the pads be capable of absorbing as much fluid as possible for a given limited small bulk. I have found that there is a critical or optimum relation between the bulk or apparent density of the mass of absorbent" fiber and the absorption capacity thereof. If, for a given size pad, too much fiber is compacted into its volume, much of the permeability of the pad to liquid is lost with a resulting decrease in absorbency. On the other hand, if such pad is not compressed or compacted, the amount of fiber in the mass may be too small to retain the required amount of fluid in the interstices thereof. Furthermore, in the case of such pads as may be used for nasal or vaginal tampons or dental rolls, it is desirable that the fibrous mass, before use, have a substantial rigidity to facilitate insertion of the tampon or roll and, in the case of such devices supplied originally in an enclosing tube, for example, such stability against expansion isdesired to avoid excessive frictional resistance toejection from the tube. It is difiicult, however, to make an unspun mass of absorbent cotton hold just the degree of compression desired.

According to this inventionan absorbent p'ad of'predetermined size is produced with a particular density such that it iscompacted yet readily permeable to fluid, by compressing a mass of absorbent fibers under conditions which produce a stable set in the fibers without destroying their elastic memory, whereby, when they'ar'e wet with fluid, the set is released and the fibers tend to return to the formwhich they had before compression. In order to facilitate setting of the fiber under compression to achieve the particular density or stably compressed state; the fiber is'treated according to this invention with a compression stabilizing agent as set forth below. By this treatment the fibers are given a stable set in the absorbent mass, and this set can be controlled to give a retained density in the compressed mass which corresponds" to a high degree of absorbency not obtainable with'untreated fibers.

Accordingly, a principal object of this invention'is' to:

provide an improved absorbent pad of the character described'having high absorption elficie'ncy.

Another object of this invention is to provide an improved absorbent pad of treated fibers havinga stable set under storage conditions.

Still another object of this invention is to provide an 2,845,070 Patented July as, less 2 improved method of producing an absorbent pad of the character described. 7 I

A still further object of this invention is to provide a method of improving the stability of form and dimensions ins compressed absorbent pad of the character described.

Still another object of this inventionis to increase the absorption efiiciency of absorbent pads of the character described. 7 I

A still further object of. this invention is to provide an absorbent pad of the character described with increased absorption capacity for a given bulkof absorbent fiber.

Still a further object of this invention is to provide a method andniaterials for stabilizing the form of absorbent cotton and like fibers imparted thereto by: compression of amass of unspiin fibers to a desired size and bulk or density, p

A sun further object or this inventio s to simplify the manufacture of absorbent paids and thereby to reduce their cost.

Still another object of this invention is to provide compressed absorbent pads of the character d'escribed which will retain a predetermined stable density and degree of compression upon the release of compressing forces.

Other objects and advantages of this invention will be apparent from the following description, the accompanying drawings, and the appended claims.

Inthe drawing H 4 1 Fig. 1 is an isometric view of a vaginal tampon as illus na ive of an absorbent device embodying this invention;

d i Fig. 2 is a view partly in axial section and partly in plan ofthe'taInponofFig. l. v V A U Considering an absorbent pad comprising a compressed mass of unspurr absorbent cotton fibers, it is possiblewith suchcompression to overcome the inherentresiliericy of the fibers and produce a compressed mass remains compressed after the compressing forces are released has been found, however, thatthe amount of compression of untreated fibers necessary toa'chieve such stability of form and dimensions- (i. e., toovercornel inherent resiliencyof the fibers" tending to spring back to alarger loos'eim'ass after compression) may be so great that the densityof the resultingcompr'esse'd mass precludes maximum absorbency of the pad, i. e., because it is too tightly compressed, with too little airspace between theiindividual fibers. so that it actually absorbs less fluid than a smaller amount of fiber ina less 'dense'mass p A, V

Of course the appropriate size for an absorbent padin compressed form is determined by its intended use. For

example, the size of a vaginal tampon should be determined by' how much fiber can be comfortably inserted and worn'in the vaginal cavity. It not true, however, that the more fiber which can be compressed intoa tampen" of given' size, the more fluid will absorbland retain, In fact have discovered that there is a critical density offiber'for'rnaximum absorption of-fluid, and that this not the'same density which cotton assumes after conventional compression treatment. g H

Ithas been found that the problem is somewhat analogous tame creasing of textile fabrics, in' th at both involve the-ability'of the fibers to take a set in the bent forrn produced by pressure on the fibrous mass, and in both c'as'es'the resiliency of the fiber and permeability of the fibrous mass must not be destroyed. In the present case, there is, no -creasing of a fabric desired and the primary purpose is absorbency of the pad; v V U It'has' also been found that processes heretofore employed in manufacturing such absorbent pads have achieved a stable compression, although not necessarily at -the optimum density for maximum absorption, by

utilizing very high compressive forces. By use of the compression stabilizing agents according to this invention, such compression stability can be produced with optimum density with a reasonable compression pressure. Also heretofore, it has been attempted to achieve a compression stability with such absorbent pads by conducting all or part of the manufacturing operations under rigidly controlled conditions of temperature and humidity and by maintaining both temperature and humidity at elevated levels. Such procedures are not only costly, but they necessarily involve an atmosphere which is uncomfortable for the workers and, in cases Where large amounts of absorbent cotton are stored over substantial lengths of time at elevated temperature and humidity, mold growth, etc., are encouraged in the cotton. Producing absorbent pads according to this invention eliminates such difficulties.

Satisfactory results according to this invention have been produced by treating the fibers of an absorbent cotton mass before compression with compression stabilization agents as set forth below. Such treatment enables the production of compressed absorbent pads with the desired compression stability and optimum density for a given bulk or size of fiber mass. For example, a process according to this invention permits the production and commercial operations of a stable pad of desired size and optimum density containing, for example, in a standard size vaginal tampon, as little as 2.3 grams of absorbent cotton, whereas not less than three grams of cotton was formerly required to produce a tampon of the same size and comparable stability by compression pressure alone without the use of a stabilizing agent.

The surprising results in size stability and improvement in absorption capacity obtained by treating fibers according to this invention is evidently due to the use of compression stabilization agents in amount which allows the fibers to take a set and hold it with substantial stability, but with elastic memory, so that it is released upon wetting. The compression stabilization agents according to this invention are selected primarily for the plasticizing effect on the absorbent cotton to be treated. It is thus believed that the limited plasticizing effect on the cotton fibers, before pressing so far overcomes the inherent resiliency of the fibers that a set can be given thereto which is stably held but with elastic memory. It is also believed that such set is thereafter maintained, in a state of elastic memory, upon the release of compressing force due to the presence in or on the fibers of the plasticizer in amount adapted to set as a compression stabilization agent. Without such agent, the fibers exhibit elasticity which prevents the desired set; and too much plasticizer would give elastomeric resiliency or even plasticity which would preclude the desired elastic memory.

Although I refer here to stabilization and dimensional stability, it need not be absolute. Thus, for some time after compressing, the fibers may still undergo continued or repeated variations caused, for example, by varying moisture content picked up from or given ofl to the atmosphere under varying humidity conditions, but without such dimensional variations causing excessive fiufling out or essential lack of compression stability.

Accordingly, compression stabilization agents for this invention are selected primarily for plasticizing effects on the absorbent fiber. Advantageously, such agents should possess also surface wetting properties to facilitate wetting of the fiber to release its set and giveeflect to its.

memory. This property also helps the plasticizing agent to penetrate the fibrous mass to effect plasticizing thereof.

Preferably, such compression stabilizing agents are, in addition, hydrophilic, fluid and water soluble. Especially when the absorbent pad is for body fluids, such as catamenial pads, vaginal tampons, dental rolls and the like, such agents should be aesthetically acceptable, compatible with living tissue which the device may contact in use, as well as being compatible with the fluid to be absorbed. That is, the agent should not have properties (biological, chemical or aesthetic) which are inconsistent with its intended use. For example, one agent which might be considered too germicidal for a vaginal tampon would give completely satisfactory results in a dental roll or a compressed pad for nonphysiological use. Neither should such agents be adhesive, or at least, any adhesive effect should be promptly released upon contact with the fluid to be absorbed, in order that the maximum volume of interstices between fibers within the mass should be available for fluid absorption. In general, materials which are known to facilitate and stabilize creasing of cellulosic or other absorbent fibers can be regarded as suitable for this invention it they are hydrophilic and compatible with whatever fluid is to be absorbed and whatever tissue is to be subjected to contact with the treated cotton.

Such agent is employed to modify the resiliency of the fibers so that they will retain their compressed form after the compressing forces are released (e. g, during storage before use) and yet will retain a memory of their original loose form which will be released upon wetting so that the fibers can expand to take up fluid during use, thus providing maximum absorption capacity. The materials of this invention, however, apparently act upon the fibers themselves in a manner analogous to plasti cizing to alter elastic characteristics thereof, and are to be distinguished from adhesives which merely bond or embed the fibers so as to restrain their elastic recovery.

Such compression stabilizing agents of this invention advantageously are distributed on the surface of the fiber and can be effective in minute amounts without leaving more than a microscopic or monomolecular film or deposit on the individual fibers. But this amount on the individual fibers should be strongly held or diffused into the fiber. To this end a working of the fibers, e. g., by carding and other processing steps and storage for sufiicient time to allow substantial diffusion of the compression stabilization agent into the fiber after its application and before the pressing step is advantageous.

The class of materials which have been found satisfactory include fiuid, water soluble, hydrophilic, plasticizers for cotton fiber. Some representative materials with which satisfactory results have been obtained are:

Polyoxyethylene sorbitol lanolin derivative (Atlas As noted, it is preferred that such plasticizing compression stabilization agents also possess surface tension depressing, i. e., wetting agent properties; and some wetting agents which without water would not be plasticizers may, by wetting agent action, give a compression stabilization when used with water. Duponol, Nacconol, and Aerosol noted above are all well known anionic wetting agents, while Roccal is a cationic wetting agent and glycerol monostearate is a non-ionic wetting agent. Triethyl citrate is representative of a class of plasticizers which are not classified as wetting agents.

Satisfactory results have been achieved with the above agents applied to the cotton generally in the range of from 0.1% to 20% based on the dry weight of fiber (5% moisture content), although concentrations within the range of approximately 0.25% to 1% are most advantageous. In general, additional agent beyond 1% has not shown enough improvement to justify its cost. In some cases a maximum effect is reached in the range of from 0.25%. to 1%, after which. additional. agent. may actually impair the desired effect. One or more: of. such compounds may be used, the totalconcentration being, advantageously, within these percentage ranges.

There appears to be advantage in applying. these materials duringthefinal washingbf the fiber, i. e.,.by washing with. a solution of: the agent. A. substantial proportion. of the agent will be'l'ost in the wash water buta sufficientproportion. is held on the fiber as a-film andthe subsequent treatment ofthefiber distributes mechanically any unevenness inapplication and the heat involved in drying, etc, accelerates bonding. of the agent. to the fiber.

These materials are allwater-solubleandsubstantially non-volatile, so that the properties of the treated material are not lostby evaporation.- These materials are advantageously applied. to the fibers. in water solution, although other solvents may be used and. in. some in.- stances direct applicationto thefibers without a solvent may be carried out as noted below;

For purposes of illustration, however, and: without limiting the. scope: of this invention,one'procedure will be described for forming a vaginal tampon embodying this invention and using-.Duponol C (sodium lauryl sulfate) as the compression stabilizingeagent:

An aqueous solution. of the Duponol. was prepared in 0.2% concentration (although any other. concentrations which are convenient for. the application procedure may be used). Thissolutionwas sprayed or otherwise dis. tributed over theabsorbent fiber in such. proportion that the Duponcl so applied was. within. the: range. from LOO-10%. on the air dry weight of the cotton- (i. e., weighed with, or. weightcorrectedto, approximately 5% moisture inthecottony- After. drying. andusual processing of. the absorbent-.fiber and. storageof the air dry treatedcotton for twodaysor more, this leftaresidue of approximately 0.20% to 2.0% of Duponol (on. theair dryweight of the cotton) in thecompleted tampon. blank when ready for compression.

The compression. stability. of. the. cotton: so. treated is increased significantly so.-that a compressed tampon made therefrom effectively holdsits size.

The compression stabilizing material isadvantageously applied to unspun, absorbent cotton fibers. in sliver, bats or the like before the. pads or tampons are cut, compressed, and'formed into their final shape. I

A solution of the agent is conveniently used asthe final wash solution applied tothe cotton immediately ahead of squeeze rolls through which the cotton passes as a final step prior to'drying. It has been found that approximately 100 cc. of. solution is retained-by approximately 100 grams of absorbent. cotton: after. squeezing; and the water is then evaporated. from theretained solution'.

Nacconol LAL (alkylarylsulfonate) used in. place of the Duponol inthis example gives almost identical results. Aerosol OT may be used in the same way but the concentration of the residue on the blank for the pad should be from 0.520% for best results.

In situations where the viscosity of. the-stabilizing material is sufficiently low to penetrate the mass of fibers satisfactorily (e. g., where the process is. carried out at elevated temperatures) the compression stabilizing agent may be directly applied to'the fibers, asby spraying-without dissolvingin water: or other diluent. Other solvents than water (e. g.-, alcohol) may satisfactorily be employed in the treating solution, but water is preferred because of its convenience and low cost and becausev it obviates many problems of solvent elimination or recovery.

After the solution of compression stabilizing. agent is applied, the fiber mass isdried,.e'. g., in the usual manner as by passing the cotton on a conveyor through: a drying tunnel withcirculationof warm air. Satisfactory results areobta'ined with temperatures. ranging from 240 F. at the wet end to approximately 212 F. at the dry end, with agent necessary for this invention is quite stably heldby the fibers so that, after an excess is evaporated, sub stantially no further noticeable loss occurs. Furthermore, normal storage of the product does not involve the high temperatures whichmay be used in the drying operation. It is probable that at least part; of the agent is held in a monornolecular layer on the fiber surface,.and' when a surface-activeagentis used, it aids the capillary absorbency of the compressed mass. It is also probable that a part enters the fiber by ditfusionto modify its rigid elasticity so as to give it the ability to take a set with elastic memory to give compression stability at. the desired. density and consequent improved. absorbency.

Evaporation losses, if any, should, of course, be considered in determining the amount of treating material applied to achieve the desired stabilizing agent concentration on the fibers of the finished absorbent. pads.

After the uncut and unformcd bats of absorbentcotton fibers are completely processed and treatedwith the com.- pression. stabilizing agent. as noted above, the. bats are cut into pads, e. g-., tampon. blanks, and compressivelyformed into a desired size and shape by conventional means-for example, between. conventional compression diesby methods well known in the art. By way ofillustration,-a convenient method of forming absorbent cotton. fibersinto a compressed generally cylindrical tampon is indicated in the patents to Voss, No. 2,076,389, April 6, 1937, and McLaughlin No. 2,416,706, March 4, 1947.. As shown by these patents, the loose cotton bats are fedin between compression dies which. impart the desiredshape and degree of compression (for the desired density of the compressed tampon).

While still under the compressing force ofthe dies, the tampon is ejected into a cylindrical chamber. where. the'compression and shape of the tampon are, maintained and where heat is applied to set the cotton fiber. mass in compressed form. The compressive force used ispreferably such that the finished tampon. has a-self-sustaining or unrestricted density of 0.3 to 0.7 gram per cubiccentimeter.

As has been noted above, an absorbent cotton tampon made by mere compression and heating. to the samedegree Without the treatment of this invention would have atendency to expand to a size greatly. in excess: of the compressed size. upon being ejected from the heated chamber mentioned above; and if it is held by a tubular container its pressure against the walls would make it difficult to'eject. If such untreated cotton is compressed enough to hold its form it is too densefor the desired absorbency. Utilizing the principles of this invention, however, the inherent elasticity of. cotton. fibers ofthe tampon is overcome and the tampons are caused to. retaintheir compressed configuration so that, upon ejection from the compressing apparatus and after compressing. and retaining forces are removed, the tampon will still substantially retain its compressed condition without excessive pressure against the container. Yet, the effect. of compression stabilizing-materials of this invention-issuch that the compressed condition-is released by wetting. or direct contact of the fibers with. body fluid, and. such wetting or spreading of the fiuid over thefibers isdirectly, promoted bythe surface-active compression. stabilizing. agent.

Although one example of the method of this invention has been described in detail above using Duponol as illustrative of the various resiliency modifying and size stabilizing materials with which satisfactory results have been obtained, it will be understood that other materials or substances including those specifically set out above may also be advantageously used according to this invention. Similarly, compressing techniques other than that mentioned by way of illustration may be used in a process embodying this invention, which is not limited to the specific apparatus, techtniques, concentrations, or materials set forth above.

Satisfactory results have been obtained using such other materials as compression stabilizing agents in concentrations of from 0.1% to If the fibers are plasticized to the point that they fuse or mold under compression or become rubbery or too resilient to take a set, the proportion of plasticizer should be reduced. Although the compression stabilization agents generally, such as these set forth above, have been found to give satisfactory results in the residue concentration ranges set forth, approximately 0.25 (based on air-dry weight of fiber treated) may be considered a satisfactory minimum concentration and approximately 2% a maximum concentration for general use in commercial operations.

It will also be understood that the compression stabilizing material may satisfactorily be applied to the cotton fibers at various stages in the processing thereof other than during the last washing step.as described above. These agents, with or without dilution may be applied as a spray or vapor in conventional carding or other steps with the advantage that the fibers are subjected to rubbing along their surfaces which blends the agent with the fibers, and thus overcomes inequalities or non-uniformity in application.

It has been noted that chemical agents of the character set forth, when applied to cellulose fibers according to this invention apparently become more strongly held by the fibers the longer they remain in contact therewith; so that the treatment appears to be more than a mere temporary inter-fiber entrapment of treating material by the mass of fibers. The setting produced according to this invention suggests that some alteration of the fibers themselves, or at least an alteration in their inherent elastic properties takes place. But the fact that the fiber mass expands upon contact with body fluid indicates that any structural or chemical alteration or surface phenomenon that may occur as a result of the described treatment is a releasable one.

I claim:

1. The method of making an absorbent pad of absorbent cotton fibers, which comprises the steps of distributing onto the fibers a hydrophilic water soluble plasticizer therefor, working the fibers to distribute the plasticizer, storing the cotton for a substantial time, compressing a predetermined weight of said cotton into a predetermined volume and holding it under compression until the fibers are set in forms corresponding to a desired density.

2. The method of making an absorbent pad of cotton fibers, which comprises the steps of distributing onto such fibers at least about 0.1% of their weight of a hydrophilic water soluble plasticizer therefor, compressing a predetermined weight of said fibers into a predetermined volume and holding the resulting mass of fibers under said compression until set in forms corresponding to an apparent density, upon release of compression, approximately 0.3 to 0.7 gram per cubic centimeter.

3. The method of making a compressed absorption device of absorbent cotton fibers which comprises the steps of distributing onto said fibers a hydrophilic water soluble wetting agent plasticizer therefor as a compression stabilization agent efllecting plasticizing of said fibers for modifying said inherent resiliency thereof, compressing a predetermined weight of said fibers to a predetermined volume, subjecting said fibers to heat during said compression step rapidly driving moisture from said fibers, and maintaining said compressed fibers under compression until set.

4. The method of making a compressed absorption device of a mass of cotton fibers which comprises the steps of distributing onto said fizers throughout said mass a solution of a hydrophilic water soluble plasticizing wetting agent for said fibers, drying said fibers leaving deposited thereon said plasticizing wetting agent in an amount in the range 0.1% to 20% of the air dry weight of said fibers, compressing a predetermined weight of said fibers into a predetermined volume corresponding to a density which provides capillary porosity for ready absorption of fluid and holding the resulting mass of fibers under said compression until set in said compressed form.

5. The method of making a compressed absorption device of a mass of cotton fibers which comprises the steps of distributing onto said fibers throughout said mass a solution of a hydrophilic water soluble plasticizing wetting agent for said fibers, drying said fibers leaving deposited thereon said plasticizing wetting agent in an amount approximately 0.1% to 20% of the air dry weight of said fibers, compressing a predetermined weight of said fibers to a predetermined volume corresponding to a density which provides capillary porosity for absorption of liquid, subjecting said fibers to heat during said compression step, and maintaining said fibers under compression and heat until set in said compressed form.

6. The method of making a compressed absorption device of a mass of cotton fibers which comprises the steps of distributing onto said fibers throughout said mass a solution of a hydrophilic water soluble plasticizing wetting agent for said fibers, drying said fibers leaving deposited thereon said plasticizing wetting agent in an amount approximately 0.25% to 1% of the air dry weight of said fibers, compressing a predetermined weight of said fibers to a predetermined volume corresponding to a density which gives the mass a capillary porosity, subjecting said fibers to heat during said compression step, and maintaining said fibers under compression and heat until set in said compressed form.

7. The method of making a compressed absorption device of a mass of cotton fibers which comprises the steps of distributing onto said fibers throughout said mass a solution of a hydrophilic water soluble plasticizing wetting agent for said fibers, drying said fibers leaving deposited thereon said plasticizing wetting agent in an amount approximately 0.1% to 20% of the air dry weight of said fibers, compressing a predetermined weight of said fibers to a predetermined volume corresponding to a density which gives the mass a capillary porosity, subjecting said fibers to heat during said compression step, and maintaining said fibers under compression for approximately 20 to 40 seconds at about 70 to C. to set them in said compressed form.

8. An absorption device of the character described for fluid absorption comprising as a fluid absorbing means a compressed mass of absorbent cotton fibers, said mass having a self-sustained density in the range of approximately 0.3 to 0.7 gram per cubic centimeter, and said fibers carrying at least 0.1% of a water soluble hydrophilic plasticizer therefor effecting stable compression at said density.

9. An absorption device of the character described for fluid absorption comprising as a fluid absorbing means a compressed mass of absorbent cotton fibers, said fibers carrying distributed thereon at least 0.1% of a water soluble hydrophilic plasticizer therefor, and said compressed mass having a self-sustaining density less than the self-sustaining density of said fibers without said plasticizer providing capillary porosity.

10. An absorption device of the character described for fluid absorption comprising as a fluid absorbing means a compressed mass of absorbent cotton fibers, said fibers carrying thereon a Water soluble fluid hydrophilic plasticizing wetting agent therefor and a minute layer of moisture effected by said Wetting agent for temporarily plasticizing and decreasing said inherent elasticity of said fibers.

11. An absorption device of the character described for fluid absorption comprising as a fluid absorbing means a compressed layer of absorbent cotton fibers, said fibers holding theron approximately 0.1% to 20% by weight of a water soluble, hydrophilic, plasticizing wetting agent 10 therefor, and said compressed mass having a self-sustaining density of approximately 0.3 to 0.7%.

12. An absorption device of the character described for fluid absorption comprising as a fluid absorbing means a compressed mass of absorbent cotton fibers, said fibers 5 2,440,141

carrying firmly held thereon approximately 0.25% to 1% by Weight of a water soluble, hydrophilic, plasticizing Wetting agent therefor, and said compressed mass having a self-sustaining density of approximately 0.3 to 0.7%.

References Cited in the file of this patent UNITED STATES PATENTS 2,067,497 McCardle et a1. Jan. 12, 1937 2,076,389 Voss Apr. 6, 1937 2,298,424 Schreiber Oct. 13, 1942 2,340,311 Donovan Feb. 1, 1944 2,416,706 McLaughlin Mar. 4, 1947 2,437,265 Manning Mar. 9, 1948 Donovan Apr. 20, 1948 

1. THE METHOD OF MAKING AN ABSORBENT PAD OF ABSORBENT COTTON FIBERS, WHICH COMPRISES THE STEPS OF DIS-
 8. AN ABSORPTION DEVICE OF THE CHARACTER DESCRIBED FOR FLUID ABSORPTION COMPRISING AS A FLUID ABSORBING MEANS A COMPRESSED MASS OF ABSORBENT COTTON FIBERS, SAID MASS HAVING A SELF-SUSTAINED DENSITY IN THE RANGE OF APPROXIMATELY 0.3 TO 0.7 GRAM PER CUBIC CENTIMETER, AND SAID FIBERS CARRYING AT LEAST 0.1% OF A WATER SOLUBLE HYDROPHILIC PLASTICIZER THEREFOR EFFECTING STABLE COMPRESSION AT SAID DENSITY. 